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Emergence of the Southeast Asian islands as a driver for Neogene cooling

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PNAS October 13, 2020 117 (41) 25319-25326; first published September 24, 2020; https://doi.org/10.1073/pnas.2011033117

  1. Edited by Dennis Kent, Lamont-Doherty Earth Observatory, Palisades, NY, and approved August 25, 2020 (received for review May 29, 2020)

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Figures

  • Fig. 1.
    Fig. 1.

    A schematic representation of the silicate weathering component of GEOCLIM in a single profile at steady state. A rock particle leaves the unweathered bedrock with production rate Pr and transits vertically through a regolith of height h. Regolith production and physical erosion (Ep) are equal at steady state. As a particle transits upwards, some fraction of the primary phases (x) are chemically weathered (W), with the flux of dissolved Ca+Mg being W multiplied by the concentration of Ca+Mg in unweathered bedrock (XCaMg). Details of the formulation for the silicate weathering component of GEOCLIM can be found in Materials and Methods.

  • Fig. 2.
    Fig. 2.

    The emergence of the SEAIs (also referred to as the Maritime Continent in the climate-science literature) from the mid-Miocene to present. Past shorelines at 5, 10, and 15 Ma are shown in A, with associated land area summarized in B. A significant increase in area over the past 5 m.y. is coincident with cooling and the onset of Northern Hemisphere glaciation, as reflected in the benthic oxygen isotope record (35) shown in C.

  • Fig. 3.
    Fig. 3.

    Steady-state pCO2 estimates from GEOCLIM for the various scenarios discussed in the text. For each of the seven scenarios, each point represents an estimate from one of the 573 unique parameter combinations that most closely matched estimates of present-day CO2 consumption in 80 watersheds around the world (SI Appendix). The box encloses the middle 50% of the pCO2 estimates (i.e., the interquartile range), and the notch represents the median with its 95% CI. The whiskers extend to the 2.5th and 97.5th percentile values. Glaciation thresholds (36) are shown on the x axis.

  • Fig. 4.
    Fig. 4.

    Weatherability curves for the modern and “paleo-SEAIs” scenarios shown in Fig. 3. Lower expands the lower pCO2 range (x axis) of Upper. Details on how these curves were generated are described in Materials and Methods. Each of the four curves represent a different tectonic boundary condition (i.e., the reconstructed paleoshorelines of the SEAIs; Fig. 2A) and, therefore, a different global weatherability. The curves show the resulting pCO2 for a given volcanic degassing flux such that the input flux is balanced by the silicate weathering output flux. Point B represents the preindustrial, in which pCO2 is 286 ppm. The arrow from point A1 to B represents the “increase in weatherability only” scenario, in which global weatherability increases as the SEAIs emerge, but the volcanic degassing flux does not change over the past 15 m.y. In this scenario, the pCO2 decreases from the value dictated by the 15 Ma paleo-SEAIs weatherability curve (568 ppm). The arrow from point A2 to B instead represents the “decrease in degassing only” scenario, in which global weatherability remains the same as the preindustrial, but the same change in pCO2 as the “increase in weatherability only” scenario is achieved by decreasing the volcanic degassing flux from a value ∼13% greater than the preindustrial. The arrow from Point A3 to B represents the “increase in weatherability and degassing” scenario, in which a change in pCO2 from 400 to 286 ppm is achieved by increasing both global weatherability from our 15-Ma tectonic boundary condition and the volcanic degassing flux from a value ∼7% smaller than the preindustrial flux.

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Emergence of the Southeast Asian islands as a driver for Neogene cooling
Yuem Park, Pierre Maffre, Yves Goddéris, Francis A. Macdonald, Eliel S. C. Anttila, Nicholas L. Swanson-Hysell
Proceedings of the National Academy of Sciences Oct 2020, 117 (41) 25319-25326; DOI: 10.1073/pnas.2011033117
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Proceedings of the National Academy of Sciences: 117 (41)
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